The present invention is related to a mobile information apparatus such as a notebook computer, a personal digital assistant (PDA), a cellular phone, a digital still-video camera (DSC) and a digital video camera (DVC), or a portable AV apparatus. The present invention is related particularly to a method for optimizing the charge state (which is also referred to as the SOC) of the rechargeable battery built into the mobile information apparatus.
The present invention is further related to a server that can carry out data communications with battery-powered electrical apparatuses on a network. The present invention is related particularly to a method using the server to optimize the charge state of the rechargeable battery built in each of the battery-powered electrical apparatuses on the network. Here, battery-powered electrical apparatuses include, for example, power tools such as a power drill, a power saw, and a power mower; household electric appliances such as a flashlight, a cordless cleaner, a cordless iron, an electric razor, and an electric toothbrush; emergency appliances such as a fire alarm, an emergency light, a burglar alarm, and an uninterruptible power source (UPS); in addition to the above-described mobile information apparatuses.
Most of the battery-powered electrical apparatuses have the charger. A user connects those battery-powered electrical apparatuses to the commercial AC power supply when not in use, thereby being capable of charging built-in rechargeable batteries without taking them out. Thus, the user can smoothly use those battery-powered electrical apparatuses without any trouble about mating and demating of the rechargeable battery.
Conventional battery-powered electrical apparatuses charge the rechargeable batteries usually until fully charged. Here, a fully charged condition is defined as a condition of a rechargeable battery charged to the substantial maximum capacity. The conventional battery-powered electrical apparatuses further maintain the rechargeable batteries in the fully charged condition by compensation for the self-discharge of the batteries with a continuous charge. Thus, at the time of the next battery-powered operation, the operable time or the available electric power is set at the maximum in substantially all cases.
However, a rechargeable battery generally deteriorates when maintained in the fully charged condition for a long time by a continuous charge. In other words, the upper limit of the battery capacity reduces. The degree of the deterioration, that is, the reduction tendency of the upper limit of the battery capacity (which is hereafter referred to as the continuous charging characteristic) varies among types of rechargeable battery. For example, a nickel-cadmium (NiCd) storage battery keeps a long life under the continuous charge. As for a lithium ion (Li-ion) rechargeable battery, when maintained in the fully charged condition, a number of lithium atoms are continuously concentrated into the graphite layer at the negative electrode and damage the graphite layer. As a result, the Li-ion rechargeable battery deteriorates by the continuous charge. The deterioration is particularly severe under high temperature conditions. When a notebook computer is driven with a commercial AC power supply, for example, the built-in rechargeable batteries are continuously charged under the conditions where the CPU and others generate an intense heat. The life is remarkably shortened when the rechargeable batteries are a lithium rechargeable battery. Accordingly, it is generally undesirable to maintain rechargeable batteries in the fully charged condition across the board, independently of the types and the use conditions of the battery-powered electrical apparatuses.
Conventional battery-powered electrical apparatuses include one that can maintain the charge state of the rechargeable battery at the full charge or lower levels. One example is disclosed in Published Japanese patent application No. 2001-327092 gazette. A notebook computer disclosed in the gazette monitors the remaining capacity of the built-in rechargeable battery. A charge operation is started when the remaining capacity falls below a predetermined lower limit. On the other hand, a charge operation is finished or a discharge operation is started when the remaining capacity exceeds a predetermined upper limit. Thereby, the charge state of the rechargeable battery is maintained within the range between the upper and lower limits. Here, the upper and lower limits of the remaining capacity are changed in response to the charge mode chosen by a user. When a usual charge mode (the normal mode) is chosen, for example, the upper limit of the remaining capacity is assumed to be the battery capacity under the fully charged condition, and the lower limit is set at 95% of the battery capacity under the fully charged condition. When a charge mode (the preservation mode) is chosen in order to keep the rechargeable battery in a non-use state for a long time, the upper and lower limits of the remaining capacity are set at 80% and 50% of the battery capacity, respectively.
Other examples are disclosed in Published Japanese patent application No. 2002-51478 and No. 2002-78222 gazettes. Both of the battery-powered electrical apparatuses disclosed in those gazettes use Li-ion rechargeable batteries, and perform a constant voltage and constant current charge operation to the Li-ion rechargeable batteries. In the constant voltage and constant current charge operation, first, the amount of the charging current is maintained at a predetermined value by a constant current control. The battery voltage rises in the period of the constant current control. When the charge process proceeds and then the battery voltage reaches a predetermined value (which is hereafter referred to as a control changeover voltage), the constant current control is changed to a constant voltage control, and the charge voltage is maintained. The charging current gradually reduces in the period of the constant voltage control. When the charging current falls below a predetermined threshold value (which is hereafter referred to as a charging end current), the charge operation is broken off. The battery-powered electrical apparatuses disclosed in Published Japanese patent applications No. 2002-51478 and No. 2002-78222 gazettes can reduce the control changeover voltage and/or increase the charge end current, thereby allowing a sufficiency rate of charging of the rechargeable battery, that is, the charge state of the rechargeable battery at the end of the charging to reduce from the full charge.
For the battery-powered electrical apparatus according to the above examples, a user chooses a charge mode or a sufficiency rate of charging appropriate to the use conditions. For example, at the time of the drive with the commercial AC power supply, the user usually chooses the preservation mode or lowers the sufficiency rate from its maximum value. Thereby, the charge state of the rechargeable battery is maintained lower than the full charge, and then the deterioration of the rechargeable battery is suppressed. On the other hand, when a battery-powered operation is scheduled near at hand, the user chooses the normal mode or raises the sufficiency rate to its maximum value. Thereby, the rechargeable battery is fully charged, and then, the operable time or the available electric power at the next battery-powered operation is set substantially at the maximum. Thus, the battery-powered electrical apparatuses according to the above examples can maintain the life of the rechargeable battery long enough and maximize the utilization of the battery capacity.
For the conventional battery-powered electrical apparatus according to the above examples, the user has to judge the changeover timing of the charge mode and the set value and change timing of the sufficiency rate. In particular, the user has to optimize the charge state of the rechargeable battery in order to realize the maintenance of the long life of the rechargeable battery and the maximum use of the battery capacity at the same time. However, the optimum charge state of the rechargeable battery changes, depending on various factors such as the type of the rechargeable battery, the state of deterioration of the battery, the type of the battery-powered electrical apparatus, and the frequency of use of the apparatus under the battery-powered operation. Accordingly, it was difficult for the user to suitably judge the timing of changeover between the normal mode and the preservation mode, and the change timing and the set value of the sufficiency rate. In particular, when the single user uses a variety of the battery-powered electrical apparatuses, the user has to set the charge mode or the sufficiency rate for each of the apparatuses, and this is a great burden for the user.